1. Field of the Invention
This invention relates to a method for automatically measuring the eccentricity of core wires of welding rods.
2. Description of the Prior Art
As shown in FIG. 1, welding rods consist of a cylindrical metallic core wire 1 and a coating composition (flux) 2 covering the circumference of the metallic core wire with as high a concentricity as possible.
In the manufacturing process of welding rods of this sort, the core wires are more or less eccentric with the outer periphery of the flux. The eccentricity e is prescribed by Japanese Industrial Standards to be ##EQU1##
As shown in FIG. 1, the various symbols in the foregoing formulas represents
a: Maximum thickness of coating PA0 b: Minimum thickness of coating PA0 d: Core wire diameter PA0 D: Coating diameter PA0 a-b: Variation in coating thickness PA0 a-b/2: Eccentric deviation
As for the standard for controlling the degree of eccentricity, for example, the variation in wall thickness (eccentric deviation), (a-b) can be expressed by a function of the eccentricity e, the diameter d of the core wire 1 and the diameter D of the flux 2 according to the foregoing formula, as follows. ##EQU2##
Thus, the quality of welding rods can be controlled by measuring the value of (a-b).
On the other hand, these sorts of welding rods are produced at an extremely high speed, for instance, at a speed of 1,500 rods/min, so that it has been difficult to measure the eccentricity of individual rods automatically. The current procedure of quality control is intended to measure the eccentricity by sampling inspection during or after the manufacturing process.
However, in the production of welding rods. The eccentricity and the direction of eccentric deviation of extruded welding rods are not uniform and in some cases vary from one to another even in an arbitrary number of consecutive rods of a population. Therefore, in order to maintian high quality in the welding rods, it is desirable to increase the sampling number or to inspect all of the produced welding rods, notwithstanding the various problems which are encountered in the conventional methods of eccentricity inspection as will be stated hereinabove.
The known methods concerning the measurement of eccentric deviation or variations in the coating thickness of welding rods are classified into methods using a microscope and methods using an electromagnetic eccentric meter. The former resort to a destructive inspection which is troublesome and destroys the sampled welding rods even if they are of passable quality. Therefore, this method is by no means applicable to total inspection and, even in a sampling inspection, invites a reduction of the yield of the products.
In the latter methods, a sample welding rod is gripped at arbitrary positions by a pair of measuring heads which are provided between two mounting tables, and the sample rod is rotated by hand while checking for variations in the coating thickness by contrast with variations in the difference of impedence between the two detecting heads. This method depends on manual operation and thus cannot be used for automatic inspection nor for welding rods having core wires of non-magnetic material nor of flux containing ferromagnetic powder.